Photoelectric device



Nav. 17, 1936. J. H. DE BQER ET AL,

PHOTOELECTRI C DEVICE Filed OCL. 28, 1951 www 4.

INVERTOR DE [BOER W C VAN GEEL Y Patented Nov. 17, 1936 UNITED STATES PATENT OFFICE PHOTOELECTRIC DEVICE Application October 28, 1931, Serial No. 571.5618` In the Netherlands October 28, 1930 1 Claim.

A photoelectric device has previously been proposed which contains an electrode consisting at least partially of a photoelectric substance and separated from a further electrode of electrically 5 conducting material by a layer containing one or more insulating solid substances. When the photoelectric electrode, which may consist advantageously of one or more alkali or alkaline earth metals, is subjected to light or similar radiation I there is produced between the two electrodes a potential difference which is dependent upon-the intensity of the radiation and which can produce a current in an external circuit to which the electrodes may be connected. In this case the current l flows through the separating layer which may consist of a chemical compound of the metal of which one of the electrodes is made.

In addition, it is found that the separating layer may frequently consist of one or more solid semi- 20 conductive substances.

A photo electric substance is to be understood to mean a substance adapted to emit electrons on being subjected to radiation.

The invention has for its object to improve a 25 photoelectric device of this kind so as to increase its usefulness.

A photoelectric device according to the invention contains a photoelectric electrode which is separated from a. cooperating electrode by a layer 30 consisting essentially/of one or more insulating or semi-conductive solid substances and a layer containing av fluorescent substance, the layers being sandwiched between the electrodes, andthe two electrodes and the intermediate layer being placed 35 upon and in contact with one another. A uorescent substance is to be understood to mean a substance adapted to emit fluorescent rays on being struck by electrons. These fluorescent rays may be either visible rays or invisible rays, for exi 40 ample X-rays or ultraviolet rays. The photoelectric electrode being subjected to radiation, a potential difference is produced between the electrodes of the device and this potential difference may bring about a current of electrons flowing 45 between the two electrodes. In this case the electrons impinge on the fluorescent substance and bring it to fluorescence. This may be made available in different ways.

The fluorescent rays maybe caused to react on 50 the photoelectric electrode and for this purpose the layer which separates this electrode from the fluorescent substance and which consists essentially of an insulating or a semi-conductive substance should be made of a substance and be given 55 a. thickness such that this separating layer is (Cl. Z50-41.5)

transparent to the fluorescent light. This light may increase the intensity of the radiation to which the photoelectric electrode is subjected so that the potential difference produced and the current thereby brought about are amplified. In 5 this case the photoelectric substance and the fluorescent substance must be such that the uorescent light is photoelectrically active on the said substance. If the fluorescent substance consists for example of zinc sulphide or zinc silicate, the photo electric electrode may be of caesium. If the electrode is of potassium, the fluorescent substance may be scheelite (calcium tungstate) or barium platinum cyanide.

If the electrode adjacent the layer containing the fluorescent substance is rendered transparent to the uorescent light produced, the fluorescent rays may be causedy to impinge on another photoelectric electrode in a second electrode system so that in the second electrode system with which this latter electrode is associated a potential difference and a current may be produced which are greater than the corresponding magnitudes generated in the first electrode system.

If a fluorescent substance is used which when fluorescent emits ultraviolet rays, the electrode adjacent this substance may advantageously be of silver, which is readily transparent to a denite band of ultraviolet rays. y

If the electrode adjacent the fluorescent layer is transparent to the fluorescent light, the device may successfully be used for making photographic exposures. If a light image is thrown on to the photoelectric electrode, the current of electrons emanating from any point of this electrode will be dependent upon the intensity of the exposure of this point, hence the intensity of the fluorescent light will vary from point to point on the fluorescent layer. The intensity of the fluorescent light produced in a determined portion of the iiucrescent layer will be proportional to the vintensity of the exposure of the oppositely situated portion of the photoelectric electrode so that the fluorescent image produced corresponds to the primary light image.

This fluorescent image can be recorded, for example, on a photographic plate. The fluorescent substance may be a substance the fluorescent rays of which are highly active on the photographic plate, or in other words the fluorescent image can be adapted to the photographic plate which renders it frequently possible to make satisfactory exposures of dim images.

By applying between the electrodes of the device a potential difference cf sufllcient value it bi is possible to increase the luminous intensity of the iluorescent image so as to strengthen the light image. If desired, this image may rst be thrown on to a photoelectric electrode of a further or second electrode system and be subjected there to a second amplification. -A multiple amplification is thus possible.

In order to avoid any distortion of the image, care should be taken that the fluorescent rays cannot react on the photoelectric electrode. This can be ensured by a suitable choice of the photoelectric substance and the fluorescent substance. Thus, for example, the iluorescent rays of para-oxybenzoic acid are not photoelectrically active on caesium. In the majority of cases, however, use may be made of iluorescent substances the uorescent rays of which are active on the photoelectric substance used, as in the majority of cases a penetration by the uorescent rays of the photoelectric electrode will be prevented by the separating layer which consists of an insulating or a semi-conductive substance. It

is frequently preferable that the electrode which is transparent to the fluorescent light and which for this purpose must often be made very thin should be carried by an insulating layer which therefore is also made transparent to the fluorescent light. If this light contains, for example, ultraviolet rays, the layer may be made of quartz. If the insulating layer is formed by a portion of the wall of the device, the advantage is obtained that the fluorescent substance is close to the wall of the device so that the bodies on which the fluorescent light has to act may be external to the photoelectric device proper.

If the uorescent rays have to strike, for example, a photographic plate, this plate may be arranged in contact with or at a short distance from the particular wall portion. If it is necessary that the uorescent rays should strike a photoelectric electrode of a secondary electrode system, this system may be arranged in an envelope other than that of the primary electrode system. It is, however, also possible and frequently preferable to arrange both electrode systems in a single envelope.

Preferably, the'device according to the invention is provided with such a contact member for the photoelectric electrode that the points of contact between this member and the photoelectric electrode are distributed about the surface of this electrode. This ensures a uniform operation of the entire electrode surface and in the case of a uniform exposure the same potential difference in any parts of the electrode system is excited.

In order that it may not interfere with the exposure of the photoelectric electrode, the contact member may be made of a metal network. It is also possible for the contact member to be formed by a metal layer transparent to the rays which are active on the photoelectric electrode.

In order that the invention may be clearly understood and readily carried into effect, it will be set out more fully by reference to the accompanying drawing wherein:

Figure 1 represents by way of example a photoelectric device according to the invention.

Fig. 2 is an enlarged sectional view of the ei'- iective layers of the photo-electrically sensitive portion of the device.

The device shown has an envelope l of glass or tial volatilization of a platinum wire that may be arranged in the device but which is not shown in the drawing. 'I'his volatilization of the platinum is carried out after the device is exhausted.

The platinum layer 3 is coated with a layer l consisting of a substance which when struck by electrons emits fluorescent rays. This layer may be, for example, of zinc sulphide or zinc silicate or of any of the other fluorescent substances hereinbefore mentioned. 'Ihe fluorescent substance may be applied to the platinum layer by volatilization. The platinum layer 3 is rendered so thin that it transmits the fluorescent rays of the fluorescent substance used;

The fluorescent layer l has applied to it a layer 5 which consists essentially of an insulating substance. For this purpose, first a little barium is vaporized within the device, which may be effected, for example, by decomposition of a suitable compound, for example, of barium azide, or by reduction of barium compound, for example, oi barium oxide by means of magnesium. The barium volatilized is precipitated in a thin layer on the fluorescent substance and by the admission of oxygen into the device is converted into barium oxide which is an insulator when cold. After removal of the excess oxygen, a new supply of barium is introduced into the envelope so that a thin layer of barium 6 is formed on the layer of barium oxide. This barium layer constitutes one electrode of the device.

The contact member of this electrode consists of a thin platinum layer 1. This platinum layer may be formed by volatilization of a platinum wire, whereupon it may form wholly or partly an alloy with the barium. Care is taken that the platinum layer is thin enough to be transparent to the rays which are photoelectrically active on the barium layer.

'I'he electrode 3 of the device is connected t0 a leading-in wire 8, whereas the platinum layer 'l is connected to a spring contact 9. 'I'he wires 8 and 9 are connected to the source of current III.

The wall of the device has sealed in it a lens Il. If a light image is thrown through this lens on to the platinum layer 1, the light rays penetrate on to the barium layer 6. As set out hereinbefore, a current of electrons is thus brought about at every illuminated point of the electrode system, the intensity of said current being proportional to the exposure of the photoelectric electrode in that point. The electrons bring the fluorescent substance to iluorescence so that a fluorescent image is produced which corresponds to the primary light image thrown on to the photoelectric electrode. The intensity of the uorescent image may be increased by increasing the voltage applied to the electrodes of the device.

'I'he fluorescent rays pass outwards through the platinum layer 3 and the glass plate 2 and strike a photographic plate I2 arranged outside the photoelectric device proper and shown in dotted lines. The fluorescent substance and the photographic plate may be adapted to each other so that the photographic plate has thrown on to it an image which is more intense than the primary light image which permits of the time of ex'- posure being decreased.

If a fluorescent substance is used which radiates ultraviolet rays, the plate 2 may preferably be made of quartz. In this case the electrode I may advantageously be made of silver as silver is readily transparent to a definite band of ultraviolet rays comprised between 3000 and 3100 It is of course, obvious that the various layers enclosed within the device may be made of other substances. For example, the insulating or semiconductive layer may be, of zirconium oxide, calciumuoride, silver iodide, copper oxide and the like, whereas the photoelectric substance may advantageously be made of an alkali-metal such as caesium.

It may also be remarked that the insulating or semi-conductive layer and the uorescent layer may be more or less admixed with each other when enclosed within the device.

We claim:

A photoelectric device comprising a transparent envelope having a flat vitreous Wall, an electrode comprising a transparent layer of silver on said flat Wall, a transparent layer of a. fluorescent zinc salt on said silver layer, a transparent semiinsulating layer of barium oxide on said uo- `rescent layer, and a transparent cooperating 

